The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1887-09-17
LIGHTNING,
k,nm Chambers, Journal.

kfom Chambers Journal.
Every one is familiar with the fact that
lightning does not spring direct from cloud
to cloud or to the earth, but pursues zig
zag course. This is due to the fact that
the air is not equally humid throughout
Electricity always. takes the path which
offers least resistance to its passage. Damp
air is much better conducting medium
than dry air-coasequently the lightning
selects the dampest route avoiding the drier
strata and zonesit encounters, and advances,
now directly, now obliquely, until it reaches
the opposite cloud, where it sub-divides
into number of forks. Owing to the re-
sistance it encounters in its path, intense
heat is generated, which causes the air to
expand. Immediately after the fash, the
air again contracts with great violence and
with loud report, which is echoed and re-
echoed among the clouds. The report
reaching the ear of the listeners from vary
ing distances, is drawn out into a series,
and being still further prolonged by the
echoes, the roll of the thunder is produced.
1t is curious fact that, although the sound
of thunder is exceedingly loud when heard
near at hand, the area over which 1t is
audible is comparatively circumscribed.
The noise of oaDnonade will be heard,
under favorable conditions, at distance of
nearly 100 miles, while the sound of thun-
der does not travel over fifteen miles. The
occurrence of the thunder and lightning is,
of course, simultaneous; but as light travels
faster than sound-its passage is practically
instantaneous-the fash may be seen sew
eral seconds before the thunder is heard.
The distance of thunder may thus be ap-
proximately estimated, an interval of five
seconds between the fash and the thunder
clap being allowed to each mile.
Sheet lightning has the appearance of a
sheet of fame momentarily illuminating
part of the syk or cloud surface 1t is, in
reality, but the reflection of lightning
flashing beyond the horizon or behind the
clouds, and too great distance for the thun-
der to be audible. But the most remarka-
BILE of all the manifestations of electricity
is giobular lightning, in appearance like a
ball of fire moving leisurly along and re-
naming visible, it may be, several minutes.
Many curious accounts are related of its
vagaries One of the most interesting and
circumstantial is that given by Mr.. Fitz-
gerald, county Donegal, ireland, who saw
a globe Of fire slowly descend from the
Glendowaa mountains to the valleys below.
Where it first touched the ground It ex-
cavated hole about twenty feet square,
"as if it had been cut out with huge
knife" This was scarcely the work of a
minute. Fora distance Of twenty perches
it ploughed trench about four feet deep,
and, moving along the bank of stream, it
made furrow foot in depth, Finally,
it tore away part of tho hank five perches
in length and five feet deep, and "hurling
the immense mass into the bed of the
stream it few into the opposite peaty bank. y
The globe was visible twenty minutes and
trayersed distance Of mile, showing that
its progress was, for lightning, very slow
indeed. During thunder storms Of extreme
violence on Deeside, balls of fre are occa-
sionally seen to roll down the sides of Loch-
nagar, which are no doubt identical with
globuIar lightning.